- CFA Exams
- CFA Level I Exam
- Study Session 3. Quantitative Methods (2)
- Reading 10. Sampling and Estimation
- Subject 6. Confidence Intervals for the Population Mean

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**CFA Practice Question**

A confidence interval was used to estimate the proportion of American new car owners who purchased domestic cars. A random sample of 58 new car owners generated the following 90% confidence interval: 0.376, 0.426.

Based on the interval given, does the mean population proportion of new car owners who purchased domestic cars exceed 39%?

A. Yes. The researcher has 90% confidence in the result.

B. The researcher cannot conclude that the mean exceeds 39% at the 90% confidence level.

C. No. The researcher has 90% confidence in the result.

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**User Contributed Comments**
7

User |
Comment |
---|---|

danlan |
m=0.401, the researcher knows the mean exceeds 37.6% at the 90% confidence level. |

iceluke |
he is just sure that the value is in between with 90%, but not that the mean is greater or not |

joe3 |
Good question! |

octavianus |
I think that it is important that the question refers to the "mean population" and not the mean SAMPLE. Maybe this explains why the researcher cannot make a conclusion. |

sergashev |
good one! |

aakash1108 |
nice! |

clafuente |
Hi, someone can help me explaining with more details please? Thanks so much |